To obtain a one-way type rotary damper largely different in damper effect torque with the difference in the relative rotation direction between a housing and a rotor.

The rotor 20 is formed of a first divided member 22 and a second divided member 24 which are divided in the axial direction. On the end faces of the first divided member 22 and the second divided member 24, which are opposed to each other, there are formed end face cams 22F, 24E of a shape for axially displacing the first divided member 22 relative to the second divided member 24 by relative rotational displacement of both divided members. By axial movement of the first divided member 22 with difference in the rotation direction of the second divided member 24, a throttle flow passage 34 defined between the first divided member 22 and the inner wall of a rotor chamber 16 varies in size and the rotor 20 varies in axial length so that a difference is caused in the damper effect torque.